In reply to GHawksworth:
I've got a Rab Survival Zone Lite. Minimal design: no zip, just a drawstring. Plenty big enough for me & I'm 6ft.
Weighs 224g made of Pertex Endurance fabric. Packs very small: 25 x 11cm
Good for summer alpine bivvying, I'd say. Haven't had experience of it in heavy rain. The fabric is v. thin so I don't expect it to be very hard-wearing, but that's a trade-off with weight. Not had a problem with condensation so far.